Orientifolds, M-Theory, and the ABCD's of the Enhancon

Abstract

Supergravity solutions related to large N SU(N) pure gauge theories with eight supercharges have recently been shown to give rise to an ``enhancon'', a new type of hypersurface made of D-branes. We show that enhancons also arise in similar situations pertaining to SO(2N+1), USp(2N) and SO(2N) gauge theories, using orientifolds. Enhancons therefore appear to come in types A, B, C, and D. The latter three differ globally from type A by having an extra Z_2 identification, and are distinguished locally by their subleading behaviour in large N. We focus mainly on 2+1 dimensional gauge theory, where a relation to M-theory and the Atiyah-Hitchin and Taub-NUT manifolds enables the construction of the smooth supergravity solution and the study of some of the 1/N corrections. The role of the enhancon in eleven dimensional supergravity is also uncovered. There is a close relation to certain multi-monopole moduli space problems.

Figures (1)

• Figure 1: D$(p+1)$--branes ending on NS5--branes, in the presence of an O$(p+1)^-$--plane (central dotted line). (a) The $N$ branes and their images in the interior give an $SO(2N)$ gauge group. On the exterior, $M$ branes and their images supply matter hypermultiplets, and carry a gauge group $USp(2M)$, as the orientifold plane changes sign when it goes through an NS5--brane. (b) At large $gN$, the fivebranes will be bent, touching at an ${\rm I\!R}{\rm P}^{4-p}{=}S^{4-p}/{\bf Z}_2$, (whose double cover is a circle in the figure), the $D$--type enhançon, where the NS5--branes carry an enhanced gauge symmetry. (In case (b), for clarity, no matter branes are shown.)